Electric discharge device



Nov, 2, 1934. v. 1... RONCl ET AL ELECTRIC DISCHARGE DEVICE Filed Aug.12, 1932 L LRONC/ INVENTORS a DEPEW Malta 6. M-

A TTORNEV Patented Nov. 20, 1934 UNITED STATES PATENT OFFICE ELECTRICDISCHARGE DEVICE Application August 12, 1932, Serial No. 628,504.

9 Claims.

This invention relates to electric discharge devices and moreparticularly to an incandescible electron-emitting cathode assembly forhigh power gaseous rectifier devices.

Electric discharge devices such, for example, as mercury vaporrectifiers having an incandescible electron emitting cathode are adaptedto be highly conductive on one half or positive part of a cycleof anapplied alternating voltage, and substantially non-conductive on theinverse or negative half of the cycle. On the conductive part of thecycle, the gas or vapor is ionized and greatly increases theconductivity of the device, so that a current, which consists of a largeelectron current and a relatively small ion current, flows between theanode and cathode of the device. On the inverse or negative part of thecycle of the applied .alternating voltage, it is desirable that there besubstantially no ions between the anode and the cathode. In suchdevices, particularly those adapted to rectify high voltages and havinga large surface cathode, the end portions of the cathode tend to be at amaterially lower temperature than the remaining portions and a highpotential gradient may be extant between the end portions of the cathodeand other sharp edges of the cathode assembly, and the anode so thationization mayoccur on the negative part of the cycle of the appliedalternating voltage. As a result of such ionization, a relatively largeundesired ionization current is established between the anode andcathode with a resultant undesired current flow in a circuit associatedwith the anode and cathode of the device. This ion discharge,furthermore, deleteriously affects the cathode of the device and impairsthe operating life and efficiency thereof.

One object of this invention is to prevent ionization in high voltageelectric discharge devices on the negative portions of the appliedalternating voltage.

Another object of this invention is to improve the thermal efficiency ofincandescible electronemitting cathodes in high power electric dischargedevices.

In one embodiment illustrative of this invention, a rectifier devicecomprises an enclosing vessel having an ionizable medium, such asmercury vapor therein, and an anode and a cathode disposed incooperative relation within the vessel. The cathode may comprise aconductive ribbon coated with a material having good emissioncharacteristics and folded to form an accordion-like assembly to providea large concentrated electron-emitting surface.

In accordance with one feature of this invention, the cathode is mountedin a receptacle comprising a disc and a shell which encloses the cathodeand is provided with an aperture to allow egress of electrons from thecathode. A. plurality of heat-reflecting members are mount ed adjacentthe cathode within the receptacle and serve to confine and toconcentrate the cathode heat so that all portions of the cathode aremaintained at substantially the same temperature.

The invention will be understood more fully and clearly from thefollowing detailed description with reference to the accompanyingdrawing in which:

Fig. 1 is an elevational perspective view of an electric dischargedevice illustrative of one embodiment of this invention, with portionsbroken away .to show details of construction more clearly;

Fig. 2 is a top view partly broken away of the cathode assembly of thedevice shown in Fig. 1;

Fig. 3 is an exploded view of the cathode assembly showing theconstituent elements and the assembly 'of portions thereof;

Fig. 4 is an enlarged detail view in cross-section showing details ofassembly of the cathode support and a heat shield adjacent the cathodesupporting stem;

Fig. 5 is an enlarged perspective view of one of the supports for thereceptacle in which the cathode is contained;

Fig. 6 is an enlarged detail view partly in cross-section of the anodeassembly; and

Fig. 7 is an enlarged detail view of the unitary getter and capsulesupport embodied in the device shown in Fig. 1.

Referring now to the drawing, a high voltage vapor rectifier dischargedevice, illustrative of one embodiment of this invention, comprises an.enclosing vessel having an enlarged bulbous central portion 10 andaxially aligned cylindrical end portions 11 and 12. "The end portion 11isv are secured, as by welding, at one end to the rods 1'7 and are eachprovided at the one end with integral flanges 19. The flanges 19 aresuitably secured, as by welding, to a dome-shaped shield 20, which ispreferably of a good heat-conducting material such as nickel, disposedadjacent the press 16 andextending immediately adjacent but out ofcontact with the inner wall of the cylindrical end portion 12. Theshield 20 is provided with a peripheral flange 21 to which a pluralityof supporting wires 22 are attached. Each of the supporting wires 22carries a unitary capsule and getter support (shown more clearly in Fig.7) comprising a wire mesh cage 23 which encloses a vitreous capsule 24containing a vaporizable material 25, such as mercury. A strip of gettermaterial 26, such as magnesium, for fixing residual gases in theenclosing vessel is secured to each of the wire cages 23. In themanufacture of the device, the enclosing vessel is evacuated to a highdegree and the unitary getter and capsule assemblies are heated, as byhigh frequency induction, to vaporize the getter material 26, whichcombines with residual gases in the enclosing vessel. The unitaryassembly is then heated further to burst the capsules 24 whereby thevaporizable material 25 is liberated and deposited at the outer end ofthe cylindrical portion 12 of the enclosing vessel. During the operationof the device the material 25 is vaporized and forms a conductive vaporbetween the anode and cathode of the device.

The member 20 forms a heat shield between the cathode, to be describedin detail hereinafter, and the press and the vaporizable material andprotects the press 16 against the heat radiated from the cathode andalso protects the vaporizable material 25 so that too great a vaporpressure will not be developed in the enclosing vessel.

A peripherally flanged disc 27 which may be of nickel, is secured, as bywelding, to flanges 28 on the supports 18 and carries diametricallydisposed parallel plates 29, each of which is provided with apertures 30and integral tabs 31 disposed adjacent the apertures. A pair of parallelinsulating rods 32, such as of isolantite or magnesium oxide, extendthrough the apertures 30 and are locked in position by the tabs 31 whichare bent over the ends of the rods 32 as shown in Fig. 2. Theelectron-emitting cathode 33 comprises a wire mesh ribbon, such asnickel, coated with thermionically active materials, for example, bariumand strontium carbonates, folded to form an accordion-like structureconsisting of a plurality of closely spaced substantially parallelsections. Each of the sections is provided with apertures to allowpassage of the rods 32 therethrough, the sections being separated byinsulating spacers 34, such as lavite. The ends of the folded cathode 33are secured to end flanges on the plate 29 as shown more clearly in Fig.2. A pair of parallel plates. 35, which may be of nickel, havingreinforcing flanges 36, are disposed substantially at right angles tothe plates 31 and immediately adjacent the connected edges of thesections of the cathode. The plate 29 and 35 define heatreflectingmembers and serve to confine the heat of the cathode so that during theoperation of the device all portions of the cathode are mainof the foldsof the cathode conserve the cathode heat with a resultant high thermalefilciency for the cathode.

In order to conserve the cathode heat further, the cathode issubstantially enclosed by a shell which also may be of nickel, includinga cylindrical portion 37 secured to a peripheral flange 38 on the disc27, and an annular top portion 39 having a restricted central aperture40, the top portion being curved, as clearly shown in Fig. 3 to presenta continuous smoothly rounded surface.

The form of the shell, together with the fact that all portions of thecathode are maintained at substantially the same temperature, reducesthe potential gradient extant between the anode and cathode assembly ofthe device, and thereby reduces the tendency for the formation ofdeleterious ionic discharges, particularly on the negative portions ofan alternating potential applied between the anode and cathode of thedevice. This construction renders the device substantiallynon-conductive on the negative portion of the alternating potential andprevents the flow of undesired currents in an external circuitassociated with the anode and cathode of the device. On the positiveportions of the applied alternating potential, the device is highlyconductive and a large current, consisting in the main of an electroncurrent with a small which are connected to the supporting rods 17 atone end and are connected to each other and to a terminal plug 42 at theother end. A leading-in conductor 43 having a terminal plug 44 at oneend and insulated from the conductors 41 by insulating 'beads 45, isconnected to one end of a metallic rod 46 sealed in the center of thepress ,16 and extending therefrom. The rod 46 extends through a centralaperture in the disc 20 and is insulated from the disc 20, as shown moreclearly in Fig. 4, by a flanged insulator 47 which is held in positionby a metallic cup 48 secured, as by Welding, to the disc 20. The rod 46also extends through an aperture in the disc 27 and is insulated fromthe disc by an insulating collar or washer 49. The free end of the rod46 is attached to the cathode 33 at substantially the midpoint thereof.The cathode heater circuit, therefore, includes the conductors 41, rods'17, supports 18, disc 27, plates 29, cathode 33, rod 46 and conductor43. The cathode consists of two sections electrically connected inparallel so that a relatively low voltage source may be utilized forsupplying the heating current.

The anode 50 comprises a truncated pearshaped shell, preferably ofcarbon, having a flat base portion disposed substantially parallel tothe top or outer edges of the cathode 33, and disposed in axialalignment with the aperture 40 in the shell 37. As shown in Fig. 1, theouter surface of the anode presented to the cathode is smoothlyroundedand devoid of sharp edges so that the potential gradient and thetendency for theformation of disruptive ionic discharges is reduced.The-anode is provided with an interior hub 51 into which a metallicsupporting stub 52 is threaded, as shown more clearly in Fig. 6. Theouter end of the stub 52 is secured, as by welding, to a metallicflanged disc 53 which is supported by a plurality of rigid wires 54extending one from each of the arms of the press 15. The rigid wires 54are electrically connected to a terminal pin 55 mounted on a thimbletype insulator 56, which is secured as by cementing, to the end portion11, by a plurality of leadingin conductors 57.

The electric discharge device may be conveniently supported, as shown inFig. 1, by a metallic band 58 which is clamped about the end portion 12of the enclosing vessel by nuts and bolts 59 and terminates in anoutwardly extending bracket or arm 60 having a longitudinal slot 61therein. The slot 61 is adapted to accommodate the shank of a bolt 62carrying a wing nut 63 whereby the arm or bracket 60 may be securelyclamped to a supporting bar 64. The supporting bar 64 is mounted upon apedestal or base 65 which may be attached to a support, not shown, bybolts or screws 66.

Although a specific embodiment of the invention has been shown anddescribed, it is to be understood, of course, that various modificationsmay be made without departing from the scope and spirit of the inventionas defined in the appended claims.

What is claimed is:

1. An electrode assembly for an electric discharge device, comprising asupport, a receptacle mounted on said support, a folded ribbon cathodewithin said receptacle, and a plurality of heat-reflecting membersadjacent and substantially encompassing said cathode, said cathode beingsupported from certain of said heat reflecting members.

2. An electrode assembly for an electric discharge device, comprising astem, a support extending from said stem, a metallic receptacle mountedon said support, an incandescible cathode having a plurality of closelyadjacent sections mounted within said receptacle, and a plurality ofmetallic plates secured to and mounted within said receptacle andimmediately adjacent outer edges of said cathode.

3. An electrode assembly for an electric discharge device, comprising astem, a plurality of supports extending from said stem, a metallicreceptacle mounted on said supports, a pair of metallic plates mountedwithin said receptacle, an incandescible cathode supported between saidplates and within said receptacle, and a plurality of heat-reflectingmembers mounted within said receptacle adjacent said cathode.

4. An electrode assembly for an electric discharge device, comprising astem, a plurality of supports extending from said stem, a metallicreceptacle having a restricted opening therein mounted on said supports,heat-reflecting plates mounted within said receptacle, a plurality ofsupports extending between two of said plates, and a large surfaceincandescible cathode mounted on said supports and disposed adjacentsaid opening.

5. An electrode assembly for an electric discharge device, comprising astem, a plurality of supports extending from said stem, a plate membercarried by said supports, a hollow cylindrical shell mounted on saidplate member, a plurality of heat-reflecting members mounted on saidplate member and disposed within said shell, and a large surfaceincandescible cathode mounted within and connected to saidheatreflecting members, said supports, plate member shell andheat-reflecting members forming a leading-in connection to said cathode.

6. An electrode assembly for an electric discharge device, comprising astem, a plurality of supports extending from said stem, a metallic discmounted on said supports, a cylindrical metallic shell carried by saiddisc, a plurality of -metallic plates mounted within said shell, aplurality of rods extending between certain of said plates, and a foldedribbon cathode carried by said rods, having its edges immediatelyadjacent said plates.

'7. An electric discharge device comprising an anode, a large surfaceincandescible cathode, and a heat conserving shield for said cathodeincluding a metallic receptacle encasing said cathode and having aportion between said anode and cathode provided with a restrictedopening to allow egress of electrons, and a plurality of heat-reflectingmembers mounted within said receptacle and substantially encircling saidcathode, said cathode being supported from certain of said heatreflecting members.

8. An electrode assembly for an electric discharge device, comprising astem, a plurality of metallic supports extending from said stem, ametallic disc mounted on said supports, a pair of parallelelectricallyconductive heat-reflecting members mounted on said disc, aplurality of insulating rods extending between said members, a foldedribbon cathode carried by said rods, having its folds substantiallyparallel to said members and connected at its ends to said members, ametallic rod extending from said stem and connected to said cathodeintermediate the ends thereof, leading-in conductors connected to saidmetallic supports and to said rod,

a plurality of heat reflecting plates disposed adjacent the joined edgesof the folds of said cathode, and a metallic cylindrical shell having arestricted opening therein mounted on said disc and encircling saidheat-reflecting members and plates.

9. An electric discharge device comprising an enclosing vessel having astem, a plurality of supports extending from said stem, a receptaclehaving a restricted opening mounted on said supports, a large surfaceincandescible cathode consisting of a ribbon folded to form a pluralityof closely spaced sections mounted within said receptacle adjacent saidopening, a plurality of heat-reflecting members secured to and mountedwithin said receptacle and substantially encircling said cathode, and ananode in juxtaposition to said opening.

VICTOR L. RONCI. CHARLES DEPEW.

